Electric furnace



C. QADWELL ELECTRIC FURNACE Filed April 29,

20 5 Sheets-Sheet l ELECTRIC FURNACE Filed April 9, 1920 3 Sheets-Sheet 2 v Caawe/ 5 Patented Jan.

teas.

i a ra n e ne er/ w P i. is. N in in in CFZABLES A. CADWELL, 0F CLEVELAND, OHIO. ASSIGNOB TO .THE ELECTRIC BAIL'W'A'Y IMPROVEMENT COMPANY, OF CLEVELAND, CHIC, A CORPORATION OF OHIO.

minerals renames.

Application filed April 29, 1920. Serial 1\T0. SZYASO.

The present improvements relating, as indicated. to an electric furnace, have more particular regard to a furnace of this type adapted foro'perating with an electric cur ed to permit a crucible to be placed between the two electrodes, such crucible preferably resting on the intermediate resistor. However, by suitable modifications, such furnace may also be adapted for use as a muttle or re-hcating furnace.

The object of the present invention is to so construct andarrange the resistor element in a furnace of this type as to secure maximum efficiency from the passage of the 'current therethrough. while at the same time retaining the heating effect of the arcs produced between said resistor and the respective electrodes. A further object of the invention is to provide means for readily adjusting the position of the electrodes relativelyto the resistor. as well as for raising and lowering such electrodes incidentally to starting and stopping operation of the furnace. To the accomplishment of the foregoingand related ends, said invention, then, consists of the means'hereinafter fully described and particularly pointed out in the claims.

' The annexed drawings and the following description set forth in detail certain mechanism embodying the invention, such disclosed means constituting. however, several of'the various mechanical forms in which theprinciple of the inv ntion may be carried out.

In said annexed drawings v i Fig. 1 is a plan view of a furnace embodying my present improvements. such furnace being primarily designed for heating crucibles: Fig? is partly a side elevation and partly avertical central section of such furnace, the plane of the section being in dicated by the line 22, Fig. 1; Fig. 3 is a broken plan vienr'of the interior of said furnace illustrated in Figs. 1 and 2; Fig. 4 is a view similar to Fig. 3, but showing a modification in construction of the resistor; Fig. 5 is a broken vertical section showing still another modification in the construction of such resistor; Fig. 6 is partly a plan View and partlya horizontal section, and Fig. 6 is a sectional detail of another furnace em bodying thepresent improvements, said furnace being more particularly designed as a muffle or re heating furnace; Fig. 7 is a; horizontal section of still another form of furnace embodying my present iniprovements, such furnace likewise being adapted for use as a re-heating or muflie furnace; and Fig. 8 is a central vertical section of such last mentioned form of furnace, the plane of the section being indicated by the line 88, 7. I

Referring first of all to the construction of furnace shown'in Figs. 1, 2 and 3, such furnace will be seen to comprise an outer casing 1, preferably of sheet metal and of any desired shape and size although a convenient shape where the furnace is to be used to heat-crucibles is the elliptical one shown. are interiorly lined first with a layer 2 of suitable heat non-conducting material such as infusorial earth; then with a second thicker layer 3 of silica. The bottom of the furnace chamber thus provided is further more preferably covered with a layer l of magnesia or equivalent material, it being upon this thatthe resistor 5 is in turn placed. To facilitate the draining of spilled metal or other material from the interior of the furnace chamber, the several layers composing the bottom thereof are pierced by a hole 6 which is normally closed with a plug the space between such blocks being filled 'in by means of a third block or plate 11 resting thereon and removable when desired in-order to afford access to the-interior of The sides and bottom of this casing the chamber so as to permit of the insertion or removal of crucibles 12 or the like.

I Each of said blocks is formedwith an aperture 13 through which a carbon electrode 1 L is inserted so as to.project clownwardly with its lower end in contact or close proximity, as desired, with the resistor 5.

The construction of the mountings or hold- 7 ers for such electrodes, is clearly shown in Fig. 1, from which it will beseen that the electrode proper, which will ordinarily conl sist of a cylindrical carbon pencil, has its upper endclosely fitted in a metal tube provided with a flanged cap 16 of insulating material. I This tube 15 is held in vertically adjusted position in an outer tubular memberl7 by means of a set screw 18, whereby the position of the electrode maybe from time to time changed with respectto said ings, respectively.

Member 17 is provided with a flange 22 that in the normal position of parts rests on the upper, end of the housing and so determines the normal or operative position of the electrode carried by said member,

' any adjustment of said normal positionbe ing accomplished by loosening set-screw 18 and correspondingly raising or lowering tube 15 in which said electrode is held. For the .purpose, however, of quickly raising the electrode from such operative position or for restoring the same thereto, a series of steep helical slots 25, three in number, as shown,

is cut in the housing 19 and pins 26, one. of which is provided with a handle 27, projecting radially from member 17 into said slots so that upon rotation of said member the desired raising or lowering of the same, and thus of the electrode, is expeditiously accomplished,

The resistor 5 is principally made up of a substantial layer of material, preferably granular carbon or some similar conducting material, of relatively high resistance. The current, accordingly, in passing lengthwise through the bed of material composing the resistor generates heat, due to the resistance encountered and thus supplements the heating efl'ect of the arcs between the respective electrodes 14 and such resistor. As a matter of fact, blocks 30 of solid carbon or graphite are placed on top of the bed of granular material, thus composing the resistor, directly beneath said electrodes, and it is between the latter and such blocks that the arcs will be formed, such blocks being preferably opposed to the electrodes .in order more exactly to define or limit the lowermost positions of the latter. 4 i

lVith a resistor of the character described, I have found that the heat generated by the passage of th electric current is greatest along'the bottom of the furnacechamber', which is objectionable, 'not only because it tends to burn out such bottom, even where composed of magnesite or .e uivalenthighly refractory material, but also ecause there is a corresponding loss in efficiency. In other words, it is obviously desirable that the grieatestheat should be developed as near the top surface of the resistor as possible in order to more efficiently heat the crucible 12' or other object located in the furnace chamber. The tendency of the current thus to flow, along the bottom of the resistor is, of'

course, due to the fact that the radiation of heat is least from this portion of said resistorand the higher the temperature of the material composingsaid resistor, the lower the electrical resistance. This tendency is also in part to be attributed to the greater density of the granular material in the lower stratum of the bed, which induces a slightly greater initial current flow through such lower stratum in preference to theupper stratum of the bed. As a result, the temperature begins at once to rise in such lower stratum more rapidly than in the upper, and as the of the channel or channels which the current makes for. itself increases until nearly all such current follows the resulting incandescent streak and the material that forms the adjacent nonconducting surface is subjected to. a destructive temperature along such 'incandescentstreak.

temperature rises, the electrical conductivity To overcome theforegoing difliculty, ac-.

cordingly, I have found that it is necessary to so construct or form "the res stor 5'as to force and maintain the current flow through .the upper portion or stratum of said resistor rather than along its lower surface. To accomplish this result, briefly stated, I make said resistor of horizontallayers of different conductivity; so that the current density will be greatest in a plane raised a suitable distance above the floor, prefcrabl y approximately midway between'the bottom and top,

surfacesof the resistor: Thus, where the bed of granular material composing the resistor is an inch deep, the greatest current density should be in a plane approximately one-half inch above such floor; then the upper portion of the resistor will become at least equally as highly heated as the lower portion and will radiate heat into the space, wherein the article to be heated is located, in an efficient manner.

I have devised various means for accom-. plishing the foregoing result. Thus, as shown teams?) in Figs. 2 and 3, I simply imbed in the body of granular material composing the resistor as aforesaid, a plurality of cylindrical carbon pencils 31, such pencils being disposed trans versely of the longitudinal. axis of. the furnace, or, in other words, transversely of a line passing through the electrodes 1* The pencils preferably lie clearof the magnesite floor 4 and are, to an equal extent, covered above by said granular material. As a result, the plane in which the horizontal diameters of said pencils lie, will present a path of least resistance to the tlowof current from theone electrode to the other through the resistor, so that both initially and after the furnace becomes heated, this plane will have the greatest current density. By varying the diameter of the pencils or rods 31,, as also by varying their number and spacing,

the total resistance of the resistor to such current flow, and thus the voltage required, may be varied to suit different conditions of use. and current supply. At the same time, where, as illustrated in the figuresin utilize approximately spherical balls 32 either arranged in transverse rows as shown in Fig. 4, or otherwise distributed in the bed of granular material constituting the resistor. The result will obviously be as before the creation of a plane of lower resistance above the flooifor the passage of the current through the resistor. In Fig. 5, I show in place of the cylindrical rods, aseries of transverse bars 33 of irregular polygonal form in cross section, such bars having their maximum diameters disposed in a plane above the upper surface of the bed 4 as in the case of the two previously described structural forms of resistor.

Where itis desired to employ the furnace as a mufiile furnace or for re-heating articles, a chamber 35 extendinglongitudinally of the furnace chamber proper, as shown in Fig. 6, may be utilized. This chamber is preferably of circular cross section and may consist of an alundum tube,the respective ends of which are adapted to be closed by removable plugs 36 of the same material as the wall 3 of the furnace chamber. Transversely disposed in the space on either side of said tube 35 is a series of short carbon rods 37, preferably cylindrical in cross section just as the-rods 31 in the first described structural form of my furnace. The outer ends of theserods may be convenienetly im ,granular material the same as composes the main portion of resistor 5 in such previously described construction, and electrodes preferably in the form of plates 38 are mounted within the furnace chamber in the same general relation to the granular bed as before,

except that such plates enter into such bed, so that arcs between same and bed are smothered. As a result, upon the pasage of current through the electrodes and the composite resistor thus provided, the heating effect of the current passing'through the granular material serves to bring the chamber 35 to the proper degree of temperature. Just as in the case of rods 31, so the rods 37 provide a path of least resistance for the current throughthe resistor alongside the heating chamber 35 in a plane above the floor of the furnace chamber. 1

Instead of a longitudinally disposed heat ing chamber such as just described, one or more transversely extending chambers 40 may be utilized, as shown in Figs. 7 and 8. Said chambers 10, however, are themselves formed of hollow carbon blocks, preferably of the cylindrical shape illustrated, and of such size as to provide an e'dequate interior space for the reception of the article to be heated. These tubular carbon chambers are lined with a layer ll of alundum or similar plaster, and their open ends are adapted to be closed by means of removable plugs 42 similar to the plug36. Said chambers 40 are then imbedded in a mass of granular material. 42 and carbon electrodes here shown as extending down into such material, provide the means for passing the current through the latter. Just as in the case of the rods 31 and 37 in previously described constructions, so here, the hollow carbon members 40, which at the same time constitute the heating chambers, obviously serve to decrease the electrical. resistance for the passage of such current in a plane spaced above the floor of the furnace chamber. In other words, the path ofv greatest current density will include such chambers instead of being deflected along the floor of the furnace, where it would be relatively ineffective.

Other modes of applying the principles of my invention may be employed instead of the one explained, change being made as regards the mechanism herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

' I therefore particularly point out and distinctly.claim as my invention 1. In an electric furnace, the combination work to be heated; electrodes extending into said chamber; and a resistor exposed within said chamber and lying on the floor thereof between said electrodes, said resistor being constructed so as to provide apath of least resistance for the current in passing from one of said electrodes to the other in a plane spaced from such floor.

3. In an electric furnace, the combination of a suitable chamber providing .an exteriorly accessible space-for the reception of the Work to be heated; electrodes extending into said chamber; and a resistor exposed within said chamber and lying on the floor thereof between said electrodes, said resistor consisting of granular carbon and members of greater relative electrical conductivity imbedded therein.

4. In an electric furnace, the combination of a suitable chamber providing an exterior-. 1y accessible space for the reception of the work to be heated; electrodes extending into said chamber; and a resistor exposed within said chamber and lying on the fioor thereof between said electrodes, said resistor consisting of granular carbon and solid members of similar material imbedded therein.

5. In an electric furnace, the combination .of a suitable chamber providing an exteriorly acccsssible space for the reception of the work to be heated; electrodes extending into said chamber; and a resistor exposed within said chamber and lying on the floor thereof between said electrodes, said resistor consisting of granular carbon and solid members of .similar material imbedded therein, and haV- ing their maximum horizontal dimensions disposed 111 a plane spaced from such floor.

.6. In an electric furnace, the combination of a suitable chan'iberf providing an exteriorly accessible space for the reception of the work to be heated; electrodes extend ng into said'chamber; and-a resistor exposedwithin said chamber and lying on the floor thereof.

between said electrodes, said resistor consistmg of granular carbon and a plurality. of elongate solid members of similar material arranged transversely of the path of the current through said resistor and having their maximum diameters disposed in a plane spaced from such floor.

7 In an electric furnace, the combination trodes.

of a suitable chamber providing an exteriorly accessible space for the reception of the work to beheated; electrodes extending into said chamber; and a resistor exposed withm sald chamber and lying on the floor thereof between said eleetrodes, said resistor consisting of granular carbon, and a plurality of carbon rods arranged transversely of the path of the current through said resistor.

8. A heating unit for an electric furnace of the type described; comprising a resistor composed of granular carbon and solid members of similar material imbedded therein in non-contacting relation and, having their maximum horizontal dimensions loc'atedin a plane intermediate the top and bottom surfaces ofsaid resistor.

9. A heating unit for an electric furnace I of the type described, comprising aresistor composed of granular carbon and a plurality of elongate solid members of slmllarmaterial arranged in non-contacting relation transversely of the path of the current through-said resistor and having their maximum diameters located in a. plane intermediate the top and bottom surfaces of said re-' sistor.

10. In an electric furnace, the combination of a suitable chamber providing an exteriorly accessibles'pace for the reception of the 95 work to be heated; electrodes extending into said chamber; a .resistor exposed within said chamber and lying between said electrodes, said resistor being composed of granular carbon; and blocks of solid carbon located on said resistor adjacent the ends of said electherein; a resistor within said chamber lying between said electrodes; and means for adjusting the position of said electrodes rela-' tively to said resistor, said means each ineluding a stationary housing, a member vertically movable therein; and clamp 1neans adjustably securing the electrode to said member.

13. In an electric furnace, the combination of a suitable chamber; electrodes extending.

therein; a resistor within said chamber lying between said electrodes; and means for adjusting the position of said electrodes rela tively to said resistor, said means each including a stationary housing, a member having screw-thread connection with said housing whereby it may upon rotation be verchamber being of greater electrical conductivity than the resistor.

15. In an electric furnace, the combination of a suitable chamber; electrodes extending therein, a resistor between said electrodes; members of greater relative electrical conductivity embedded in said resistor; and a chamber embedded in said resistor transversely to a line between said electrodes and adapted to receive articles to be heated, said chamber being of greater electrical conductivity than the resistor.

Signed by me this 24 day'of April, 1920.

CHARLES A. OADWELL. 

